More than 191 tons of dynamite, detonated in less than 12 seconds, blew up the cofferdam protecting the Three Gorges Dam, which will now begin to control floods along the Yangtze River. The "world's greatest blast" created giant waves and hid the main dam in a cloud of mist and smoke. State media reported the amount of dynamite used was enough to blow up 400 10-storey buildings. The temporary dam was 580 meters long and 140 meters high. Flood season usually starts this month. Demolition of the cofferdam, built in 2003 to hold back water and generate power, raised the water level along the main dam by four meters to 139 meters.